[PATCH] drm/panel: ilitek-ili9881c: Use u8 for lane count

[Marek Vasut]

On 6/13/25 11:29 AM, Neil Armstrong wrote:
> On 12/06/2025 01:49, Marek Vasut wrote:
>> Use u8 to hold lane count in struct ili9881c_desc {} to avoid
>> alignment gap between default_address_mode and lanes members.
>> The ili9881c controller can only operate up to 4 DSI lanes, so
>> there is no chance this value can ever be larger than 4. No
>> functional change.
> 
> The u8 will still take at least 4 bytes and cpu will still
> do at least a 32bit memory access, so there's no point to change
> it to u8.
Assuming this layout:

   40 struct ili9881c_desc {
   41         const struct ili9881c_instr *init;
   42         const size_t init_length;
   43         const struct drm_display_mode *mode;
   44         const unsigned long mode_flags;
   45         u8 default_address_mode;
   46         u8 lanes;
   47 };

I wrote a quick test:

$ cat test.c
#include <stdio.h>
#include <stdint.h>

struct foo {
	void *a;
	size_t b;
	void *c;
	unsigned long d;

	uint8_t x;
	unsigned long y; // ~= lanes
};

struct bar {
	void *a;
	size_t b;
	void *c;
	unsigned long d;

	uint8_t x;
	uint8_t y; // ~= lanes
};

int main(void)
{
	printf("%d %d\n", sizeof(struct foo), sizeof(struct bar));
	return 0;
}

With which I get these results on x86-64:

$ gcc -o test test.c && ./test
48 40

And on x86 32bit:

$ i686-linux-gnu-gcc -o test test.c && ./test
24 20

Maybe there is some improvement ?